An optical transport network (OTN) is one of optical transmission technologies that have been used. OTN is being standardized by the international telecommunication union-telecommunication sector (ITU T) and the institute of electrical and electronic engineers (IEEE).
The standardization of OTN has not been completed yet. Therefore, some optical transmission apparatuses using OTN use programmable large scale integrations (LSIs) such as field programmable gate arrays (FPGAs) so as to be applicable to OTN before and after the completion of the standardization.
In some cases, the scale of a circuit used to process OTN functions is larger than the circuit scale of available programmable LSIs. In such a case, the circuit processing the OTN functions is divided into a main signal system LSI performing main signal processing and a control system LSI performing processing excluding the main signal processing, for example. Examples of the processing excluding the main signal processing include overhead processing, an interface function of a central processing unit (CPU), and reset processing. In OTN, overheads (OHs) for monitoring a network are defined. Some of the overheads are dynamically changed by being processed by the CPU.
In an optical transmission system including an optical transmission apparatus provided with such a programmable LSI, there has been a technique of updating firmware of the programmable LSI included in the optical transmission apparatus without signal interruption in the main signal system. For example, there has been a technique of downloading new firmware of the control system LSI without stopping operation of the main signal system LSI, which is a so-called uninterrupted (hitless) firmware download, and updating the firmware of the control system LSI.
As such a related art technique, there has been a technique in which the main signal system LSI retains the overhead data processed by the control system LSI before the control system LSI starts the uninterrupted firmware download and the firmware of the control system LSI is updated while the main signal system LSI retains the overhead data. In OTN, a general communication channel (GCC) and an automatic protection switching (APS) are defined as the overheads, for example. The GCC and the APS are passed from the control system LSI to the CPU and processed by the CPU when the optical transmission apparatus is operating normally. Accordingly, they change dynamically.
As an example of the related art technique, there has been a system in which an identifier is added to an original signal on a transmitting side and the resulting signal is transmitted from the transmitting side to a receiving side through two different paths while one of the signals received on the receiving side through the two paths is restored on the receiving side, so that signal paths are switched in an uninterruptible manner. There has been a system in which a GCC mode switching dedicated frame is inserted into the GCC overhead on the transmitting side and sent to the receiving side while the GCC modes are switched between by determining whether the GCC mode switching dedicated frame is inserted into the GCC overhead on the receiving side.
Japanese Laid-open Patent Publication No. 2004-266480, Japanese Laid-open Patent Application No. 2010-166254 and “Interfaces for the optical transport network (OTN)”, ITU-T G.709/Y.1331 (December 2009) are examples of the related art.